1. Field of the Invention
This invention relates to processes and apparatus for extraction of oil from a moving bed of carbonaceous materials such as oil shale.
2. Description of the Prior Art
Systems for retorting a moving bed of oil shale supported on a traveling grate by passing heat transfer gas streams through the bed to transfer heat directly to the shale are disclosed in such U.S. patents as U.S. Pat. Nos. 3,325,395 to Ban; 3,560,369 to Rowland et al; 3,644,193 to Weggel et al and 3,475,279 to Bowman. The oil shale bed is essentially static (in the sense that the shale particles do not move relative to the grates) as it is transported by the traveling grate in the systems disclosed in such patents and consequently the gas-to-solid contact is relatively low, a high drop exists in the pressure across the bed required to force the heat transfer gas streams through the bed and relatively high horesepower motors are required to drive the traveling grate chain and the fans which force the gas streams through the static bed. The low gas-to-solid contact in such "static" shale bed supported on a traveling grate substantially increases the retorting time required to distill the volatile oil products from the shale particles and consequently results in increased cracking of the oil products to less desirable gases and carbon. Further, such "static" shale beds supported on a traveling grate are susceptible to being flooded by liquid kerogen distilled from the oil bearing shale particles. Channeling occurs frequently in such "static" shale bed supported on a traveling grate, and such channeling results in: (a) loss of pressure; (b) decrease in heat transfer efficiency; and (c) recovery of less oil from the shale, thereby reducing overall efficiency. Sealing of a traveling grate supporting a shale bed against entry of oxygen and loss of heat is extremely difficult, and also a significant amount of heat energy is wasted as the traveling grate plates and grate chain return.
The system of the U.S. Pat. No. 3,644,193 patent has the above discussed disadvantages of a "static" shale bed supported upon a traveling grate and is incapable of separating different weight fractions of oil from the shale particles. The system of the U.S. Pat. No. 3,560,369 patent requires crushing, grinding and screening of the oil shale to segregate the fines; agglomerating the fines with a binder such as heavy oil; and then forming a bed on the traveling grate with the agglomerated fines occupying a middle layer between upper and lower layers of larger shale particles. The rate of transfer of heat from the radiant heaters of U.S. Pat. No. 3,475,279 to the shale particles is very low in comparison to a moving bed system wherein a heated gas steam is passed through the moving shale bed, and both retorting and sintering of the coal or shale particles occur in the same zone in this patent which does not permit close control of the temperature to which the particles are heated and also results in mixing of the desired volatile products with the combustion gases and cracking of the hydrocarbons. Ambient air rather than a nonoxidizing, or neutral gas is passed through the moving shale bed in the second, or sintering zone of the traveling grate system shown in FIG. 4 of the U.S. Pat. No. 3,325,395 and burned with the carbon in the shale particles. Such arrangement does not permit control of the oil fraction educted and also mixes the combustion gases with the desired condensable products.
Rotary kiln systems for tumbling and retorting a bed of oil shale particles are disclosed in such U.S. patents as U.S.Pat. Nos. 1,383,205; 1,423,716; 1,717,786; 2,441,386; 2,664,389; 3,496,094 and 3,844,929, but such rotary kiln shale retorting systems are incapable of separating different fractions of oil from the shale and have the disadvantages that the shale particles can only occupy a small portion of the kiln cross section, e.g., 14 percent, with the result that the tonnage capacity per unit size of apparatus is relatively low and that combustion and retorting occur in the same vessel, which results in low efficiency and in at least partial cracking of the hydrocarbons within the kiln.